Solid dielectric structures having electrode structures arranged on or embedded in the dielectric structures are known for performing plasma processes. A first electrode is positioned on a treating surface of the structure, while a second electrode is placed on the opposite side of the dielectric structure. In such a process, gas flows needed for the plasma process can be induced along a treating surface of the structure.
Dedicated plasma units having an interior electrode are also known. The interior electrode is obtained via a process wherein dielectric material is partially removed for forming a groove in a surface of the dielectric structure, an electrode deposition process and a process wherein the interior electrode is covered with dielectric material to obtain a flat dielectric surface. Again, a second electrode is placed on the opposite side of the dielectric structure. Dedicated plasma units having only interior electrodes are also known. By creating an electric field between pairs of interior electrodes a plasma process can be induced along a treating surface of the structure.
However, plasma treatments appear to be non-uniform, especially when treating structures having low or non-gas permeable materials. The gas flow is flown in a plasma zone between the structure to be treated and a treating surface of the solid dielectric structure and reacts chemically and/or physically with the structure to be treated. As a consequence, less reactive gas particles are available in a desired area that is remote from and downstream to an area where the gas enters the plasma zone, thus resulting in a non-uniform plasma treatment. The composition of the plasma activated gas is changed during its passage along the treating structure. As a result the concentration of gaseous precursor gases or particles that are added to the plasma carrier gas, may be too high in the area where the gas enters the plasma zone and too low in the area where the gas leaves the plasma zone. A too high degree of precursor decomposition may result in unwanted precursor fragments that eventually cause decreased layer quality or undesirable dust by gas phase polymerization. As partial compensation of the change of precursor gas composition along the flow path in the plasma zone, generally a high gas flow rate is being applied resulting in a significant loss of unreacted precursor gas leaving the plasma zone.